Patient bed, local coil arrangement and method to determine the position of local coils in a magnetic resonance apparatus

ABSTRACT

At least one non-stationary coil in a magnetic resonance tomography system is attached with a fastener to a displaceable bed. The fastener has a position detector incorporated therein to determine the position or a component of the position of the non-stationary coil. The portion of the position is, for example, the position along the axis of symmetry of the measurement tube.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns methods and devices to determine ordetect the position of local coils in a magnetic resonance tomographysystem.

2. Description of the Prior Art

In addition to stationary acquisition coils (for example shoulder arraycoils), non-stationary acquisition coils (for example body matrix coils)are also used in magnetic resonance (MR) tomography. During themeasurement, the measurement coils are moved into the isocenter of themeasurement tube. For this purpose, the position of the tube (primarilyalong the axis of symmetry of the measurement tube) is determined bysighting with a laser cross-hair. It is disadvantageous that such asighting is error-prone and time-consuming under the circumstances.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a design and a methodthat allow an improved position determination of non-stationary coils inan MR system. In particular the aforementioned disadvantages should beavoided.

In a bed table according to the invention for a magnetic resonancetomography system, at least one of its side edges is designed for theattachment of fasteners for coils for use in the magnetic resonancetomography system. Furthermore, a position detector determines theposition of one or more fasteners on the side edge. The position isthereby advantageously detected along one axis (the extent of the sideedge).

For example, fixing belts can be attached to the bed table according tothe invention, which fixing belts in turn themselves position the coilor coils on the body of the patient. The position of the fixing belt(and therefore of the coil) is then determined at least along the extentof the side edge using the fastening point on the side edge.

In contrast to manually determining the position by means of a lasercross-hair, the bed table according to the invention thus itselfincorporates position determination components themselves. This avoidsinvolvement of an operator/technician prior to the use of the magneticresonance tomography system, which increases the security with regard tooperating errors and the speed of the measurement process. The lasercross-hair (which can be quite uncomfortable for a patient) can also beomitted.

In an embodiment that makes use of radio-technology for identificationof the position, the arrangement according to the invention exhibits theadvantage of being more precise and insensitive to reflections thanmultiple path propagation. This can be achieved by a cable-connected orfiber-connected position determination component that itself is embodiedin the fastener.

Furthermore, compared to position determination by means of a lasercross-hair, the invention exhibits the advantage that subsequentposition changes of the coil that, for example, are due to movements ofthe patient, can be measured and taken into account. Coverage of thepatient (for example with a blanket for warming) is possible without anyproblems without hindering the position determination.

It is particularly advantageous for the bed table according to theinvention to be used together with a coil arrangement according to theinvention. The coil arrangement according to the invention for amagnetic resonance tomography system has at least one coil for use inthe magnetic resonance tomography system as well as at least onefastener by means of which the coil arrangement can be fastened on a bedtable for the magnetic resonance tomography system at a fastening point,and the coil can be aligned on the body of a patient. The fastenerfurthermore includes a position detector to determine the position ofthe coil relative to the fastening point along at least one spatialdirection.

In contrast to the simple fixing belts, the coil arrangement thus itselfcomprises possibilities to determine the alignment and the location ofthe coil relative to a base of the coil arrangement at which thefastening occurs on the bed table. The alignment and the position canthereby be determinable along one spatial direction—for example alongthe axis that is provided by the side edge of the bed table—or in allspatial directions.

The combination of the two elements according to the invention at a bedtable system allows the position of the coil with regard to the bedtable to be determined from the position of the fastening point of thefastening means at the bed table and the position of the coil relativeto the fastening point. Depending on the design of the coil arrangement,the position can thereby also be determined in three dimensions, whichis not possible or is only possible with difficulty with unmodifiedfixing belts.

Optical or capacitive proximity switches or electrical or mechanicalcontact sensors (for example) are considered for the position detectorof one or more fasteners at the side edge.

The coil arrangement can include a combination of pivot bearings and/orball-and-socket bearings for positioning the coil, which bearings enablethe alignment of (for example) telescoping devices. An exemplarycombination composed of three pivot bearings and three rods (of which atleast two are variable in length in the manner of a telescope) allows anearly free positioning of the coil over the bed table.

The elements of the coil arrangement are advantageously formed ofmaterials that do not magnetically interact. For example, plastics,glass measuring sticks and optical fibers can be used. It is likewiseappropriate to accommodate possibly necessary electronic componentsoutside of the measurement space, for example in the base of the coilarrangement that, upon fastening on the bed table, remains in the areaof its side edge.

The position detector in the coil arrangement can include at least oneoptical sensor and at least one optical waveguide. With optical sensorsit can be most easily ensured that no magnetic interaction occurs, andthus also no mutual interferences of position determination and magneticresonance measurement are to be expected.

In the method according to the invention to determine the position of acoil in a magnetic resonance tomography system in relation to a bedtable for the magnetic resonance tomography system, the coil is placedon the body of a patient and fastened on the bed table by a fastener;the position of the fastening point of the fastener at the bed table isdetermined; the position of the coil relative to the fastening point isdetermined; and from this the position of the coil is determined inrelation to the bed table.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a design for position determination of non-stationary coilsby means of telescoping fastenings,

FIG. 2 shows a design for position determination of non-stationary coilsby means of flexible belts.

FIG. 3 schematically illustrates sensors embodied in the telescopingfastenings shown in the embodiment of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a person who lies on the bed table 1 of an MR system. Twocoils, what are known as body matrix coils 5, are placed on his body.The coils 5 are fastened on respective telescoping arm systems and arepositioned by the telescoping arm systems. Each telescoping arm systemin this exemplary embodiment has three ball-and-socket joints 3. Atleast some of the ball-and-socket joints 3 can be replaced by revolutejoints. The ball-and-socket joints 3 are connected with one another bymeans of telescoping rods 4. The connection made up of telescoping rods4 and the ball-and-socket joints 3 allows the corresponding coil 5 to bevery flexibly placed in three dimensions on the body of the patient tobe examined.

In this exemplary embodiment the position of the coil 5 is nowdetermined. Instead of occurring via a manual sighting by means of alaser cross-hair, this occurs via multiple additional elements in thetelescoping arm system. In this exemplary embodiment the fastening ofthe telescoping arm on the bed table ensues flexibly via a contact point2 whose location is variable. The base of the telescoping arm system isattached at the contact point and is therefore anchored. A sensortechnology (for example via proximity sensors 7 in the bed table 1itself) allows the location of the contact point to be established. Theposition of the base of the telescoping arm system is thus known.

Additional sensors are housed in the telescoping arm system itself, asshown in FIG. 3. These are rotation angle sensors 8 and length sensors9. The rotation angle sensors 8 detect the alignment of each of theball-and-socket joints. The length sensors 9 detect the length of thetelescoping rods 4. The position of the coils 5 relative to the bedtable 1 can be determined from these data and the location of thecontact point 2.

It is advantageous for the sensors in the telescoping arm system to bedesigned so that they do not affect the measurement and are alsothemselves not magnetically affected. For example, optical systems thatoperate based on glass or plastic fibers, for example, are suitable forthis. The evaluation electronics for the sensors are advantageouslylocated outside of the MR measurement space. An arrangement at thecontact point 2 (thus in the base region of the telescoping arm system)is suitable for this purpose, for example. The evaluation electronicsreceive the data for the position of the contact point 2 at which thetelescoping arm system is attached as well as the data of the lengthsensor and angle measurement sensor and calculates the position of thecoil from these.

The telescoping arm system thus enables a three-dimensionaldetermination of the position by the rotation angle sensors and lengthsensors as well as the position of the contact point 2. In addition tothe bearing in the direction of the axis of symmetry of the measurementtube, the height above the bed table and the lateral offset from thecentral axis of the bed table can thus also be determined.

A simpler realization that allows the determination of the position withregard to the bearing in the direction of the axis of symmetry of themeasurement tube is shown as a second exemplary embodiment in FIG. 2. Inthis case the coil 5 is fastened via a fixing belt. The fixing belt 6 isfastened on the one side with the coil 5 and on the other side isattached at an attachment space 2 on the bed table 1. The attachmentposition on the bed table is in turn determined by capacitive or opticalproximity sensors, for example. Since the position of the attachmentspace in this exemplary embodiment is established at the edge of the bedtable 1, here only the position along the longitudinal axis of the bedtable 1—i.e. along the axis of symmetry of the measurement tube—isestablished.

Although modifications and changes may be suggested by those skilled inthe art, it is the intention of the inventors to embody within thepatent warranted hereon all changes and modifications as reasonably andproperly come within the scope of their contribution to the art.

We claim as our invention:
 1. A patient table for a magnetic resonancetomography apparatus, comprising: a patient platform configured toreceive a patient thereon, said patient platform comprising a pluralityof side edges; a fastener having a first end configured to hold amagnetic resonance local coil at a position relative to the patient onthe table platform, and having an opposite end configured for attachmentto one of said side edges of said patient platform; and a positiondetector incorporated in said fastener configured to emit a signal thatidentifies a position of said fastener at said side edge, said positiondetector comprising a plurality of sensors that generate informationfrom which the position of said fastener is identifiable, said sensorsbeing selected from the group consisting of mechanical contact sensorsand capacitive proximity switches.
 2. A coil arrangement for a magneticresonance tomography system, comprising: a local coil configured to atleast receive magnetic resonance signals from an examination subject; afastener having a first end connected to said coil, and a second endconfigured for attachment, at a fastening point, to a patient table onwhich the examination subject is located, said fastener comprisingtelescoping fastener elements; and a position detector incorporated insaid fastener, said position detector being configured to emit a signalidentifying a position of said coil relative to said fastening point inat least one spatial direction.
 3. A coil arrangement as claimed inclaim 2 wherein said fastener comprises a plurality of fastener elementsinterconnected for relative articulation between the fastener elementsby articulations selected from the group consisting of pivot bearingsand ball-and-socket bearings.
 4. A coil arrangement as claimed in claim3 wherein said position detector comprises a plurality of sensorsrespectively located at each articulation, each sensor detecting, andemitting a signal corresponding to, an angle between the fasteningelements at the articulation at which the sensor is located.
 5. A coilarrangement as claimed in claim 2 wherein said fastener is comprised ofnon-magnetically interacting material.
 6. A coil arrangement as claimedin claim 2 wherein said position detector comprises at least one opticalsensor that emits an optical sensor signal, and at least one opticalwaveguide in optical communication with said optical sensor, whichconducts said optical sensor signal from said optical sensor.
 7. A bedtable system comprising: a patient table having a patient platformconfigured to receive an examination subject thereon, said patientplatform comprising a plurality of edges; a local coil configured to atleast receive magnetic resonant signals from the examination subject onthe patient platform; a fastener having a first end connected to saidlocal coil and a second end fastened, at a fastening point, to one ofsaid edges of said patient platform; and a position detectorincorporated in said fastener, said position detector being configuredto determine a position of said fastening point of said fastener at saidedge of said patient platform and, from said position of said fasteningpoint, to determine a position of said local coil relative to saidfastening point.
 8. A method to determine a position of a local coil ina magnetic resonance tomography apparatus comprising the steps of:placing a local coil at a coil position relative to an examinationsubject on a patient table, said patient table comprising a plurality oftable edges; fastening said local coil to said patient table with afastener having a first end connected to the local coil and a second endfastened, at a fastening point, to one of said edges of said patienttable; incorporating a position detector in said fastener; and with saidposition detector, automatically detecting a position of said fasteningpoint at said one of said edges of said patient table and, from saidposition of said fastening point, automatically determining said coilposition relative to said fastening point and, from said coil positionrelative to said fastening point, automatically determining a positionof said coil relative to said patient table.
 9. A patient table and coilposition identification system for a magnetic resonance apparatus,comprising: a patient table having a patient platform, configured toreceive an examination subject thereon, said patient platform comprisinga plurality of edges; a local coil configured to at least receivemagnetic resonance signals from the examination subject on the patientplatform; a telescoping arm assembly comprising at least one telescopingarm having first and second ends opposite to each other, a fastenerelement configured to be fastened at a selectable fastening point alongone of said edges of said patient table; a first articulated jointconnecting said first end of said telescoping arm to said fasteningelement, and a second articulate joint connecting said second end ofsaid telescoping arm to said local coil, said first and secondarticulate joints and said telescoping arm, in combination, allowingselected, three-dimensional positioning of said local coil at a localcoil position relative to said examination subject on said patienttable; a fastening element position detector that detects a position ofsaid fastening point along said edge of said patient table; a pluralityof sensors built into said telescoping arm assembly that respectivelyemit sensor signals that collectively identify said coil positionrelative to said fastening point; and an evaluation unit incommunication with said fastening element position detector and saidplurality of sensors built into said telescoping arm assembly so as toreceive respective signals therefrom, said evaluation unit beingconfigured to identify a position of said local coil relative to saidpatient table from said position of said local coil relative to saidfastening point, and said position of the fastening point relative tosaid patient table.
 10. A system as claimed in claim 9 wherein saidplurality of sensors built into said telescoping arm assembly comprise afirst rotation angle sensor built into said first articulated joint, asecond rotation angle sensor built into said second articulated joint,and a length sensor built into said at least one telescoping arm.
 11. Asystem as claimed in claim 9 wherein said plurality of sensors builtinto said telescoping arm assembly are sensors selected from the groupconsisting of optical sensors and electrical sensors.
 12. A system asclaimed in claim 9 wherein said fastening element position detector is aproximity sensor.
 13. A system as claimed in claim 12 wherein saidproximity sensor is a capacitive proximity sensor.
 14. A system asclaimed in claim 9 wherein said fastening element position detector is amechanical contact sensor.
 15. A system as claimed in claim 9 whereinsaid fastening element is comprised of non-magnetically interactingmaterial.